An electric current sensor having the core of a ring shape, the magnetic gap formed by cutting and opening one portion of this core, and the Hall element arranged in this magnetic gap is conventionally known. The sensor is disclosed in, for example, Japanese Patent Application Publication No. 2002-296305. In this electric current sensor, the core and the Hall element are stored to a storing portion opened in the upper portion of a box body, and the interior of this storing portion is filled with a sealant of a synthetic resin material. The core and the Hall element are sealed by hardening this sealant.
In the electric current sensor, an electric current flowed to an electrically conductive member inserted into the core of the ring shape is detected by the Hall element arranged in the magnetic gap. Namely, a magnetic flux is generated within the core by the electric current flowed to the electrically conductive member, and the Hall element generates a voltage (Hall voltage) due to the Hall effect corresponding to this magnetic flux. The Hall voltage generated by the Hall element not only corresponds to the magnetic flux within the core, but also corresponds to the electric current flowed to the electrically conductive member generating this magnetic flux. Therefore, it is said that the Hall voltage is a detecting signal of this electric current value.
In this connection, for example, the electric current sensor is used to detect the electric current flowed to the electrically conductive member (bus bar) for connecting a car mounting battery of an automobile and a vehicle electric mounting article.
The core and the Hall element are first attached into the storing portion to manufacture the electric current sensor. Next, the interior of the storing portion is filled with liquid having fluidity or the sealant of a gel shape by flowing this liquid or the sealant into the storing portion or dropping (potting) the liquid or the sealant. Subsequently, the core and the Hall element are sealed and fixed within the storing portion in a state in which the core and the Hall element are positioned within the storing portion by hardening the sealant.
Here, the magnetic gap of the core is formed by cutting and opening one portion of the core. Therefore, stress generated by hardening the sealant is applied to the core, and the core of the ring shape is deformed, and the size shape of the magnetic gap is changed from a set value. Therefore, a problem exists in that accuracy and sensitivity of the electric current detection using the Hall element are reduced.
In particular, when the sealant having thermosetting property is used, large stress is generated at the thermosetting time of the sealant by a linear expansion coefficient of this sealant. Therefore, the core is easily deformed by this stress.
The sealant having small stress generated at the hardening time may be used to prevent the deformation of the core caused by hardening the sealant. However, since such a sealant is expensive, the problem of an increase in manufacture cost of the electric current sensor is caused.